Lean AFR's.......... fixed ?

Y

youngsyp

Active Member
The AFR graph I got from my run at the Surrey dyno day, showed the car was running very lean across the whole rpm range, richening up when under load but, still in the high 13 range.

After plugging in Conzult and armed with other information, the conclusion was that the fuel pressure was low (very) across the board, under load and not under load.
At the time, I had a stock fuel pump (93k miles old), being fed with full alternator voltage. Naturally, this was the first area to improve on. I've now replaced it with a 255lph Walbro pump, still being fed full alternator voltage. I also checked the fuel filter, to confirm it wasn't blocked.

I've today, checked the fuel pressure and it was around 3.3 bar with the vacuum pipe disconnected and 2.8 bar with the pipe connected. The gauge was placed, inline, between the fuel filter and fuel rail. The FPR also responded well to throttle inputs (stantionary with vacuum pipe connected obviously), with blips of the throttle, causing a 0.2 bar or so, blip in fuel pressure.

The question is, is 3.3 bar about right for 'base' fuel pressure ? As, I thought it was supposed to be 3 bar ?! Or, is that what you' expect with the higher pressure pump ?
Also, should I expect the FPR to behave, as the fuel pressure gauge shows ?

The car does feel a bit more punchy and, the exhaust emissions do smell different too (couldn't really smell them before).

I will get the car dynoed again, just to confirm AFR's are ok, Thorney Motorsport are just up the road and they have a very nice looking dyno cell, with dyno dynamics rollers !

Cheers

Paul
 
B

B1Ad3

New Member
From what ive read from the factory manual 3.3 bar and 2.8 sound right in terms of the fuel pressure.

Could it be the injectors, might need a clean ro something.
 
P

PK11NN

Guest
With the vacuum pipe disconnected = 2.94 Bar = 43 Psi

With the vacuum pipe connected = 2.45 Bar = 36 Psi

Always set it with the vacuum off, as the idle speed affects it when its not.


:) from the manual
 
Y

youngsyp

Active Member
Right to answer a few questions:

I haven't checked the fuel pump voltage under load. That shouldn't change though as, it's been 'hard wired' to the battery, with 30amp (2.5mm2) cable. !

As for the FPR being tired, I have a newer one I could swap over with it so, I might give that a try. But, if it is tired, that affectively means that, it will just run a bit richer across the rpm and load range so, I'll be safe with it ?!

Didn't check the fuel pressure before I changed to the Walbro as, I didn't have a gauge !

I'm still not convinced with the AFR issue as, they fiddled around with the probe in the exhaust on each run and, I've always had issues at MOT time when they try to take emissions readings, because they can't get the probe in the exhaust properly !

Plus, I'd be interested to know where they took a vacuum/boost reading from on the dyno as, their line didn't have a 'T' piece on it so, how did they block off the pipe the took off ?

Would the fuel pressure go up a bit because the Walbro can supply higher pressure fuel ?

Oh, and I just had to replace a fuel pipe at the weekend, because, with the age of the pipe, it couldn't cope with the new found fuel pressure it would seem !
 
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campbellju

campbellju

Moderators
Staff member
Buy yourself a WB Lambda. Under £200 and you never need to use a rolling road again.

The venturi style adapters for the exhaust do work but sometimes they don't work as well. Don't think of it as a tuning gadget but a useful tool you need for whatever car you have in the coming years.

If you're AFR's are really 13 under load then expect to see some overheated spark plug colours too.

The Walbro is a high "flow" pump, the pressure is maintained by the FPR.
 
Y

youngsyp

Active Member
campbellju said:
Buy yourself a WB Lambda. Under £200 and you never need to use a rolling road again.

The venturi style adapters for the exhaust do work but sometimes they don't work as well. Don't think of it as a tuning gadget but a useful tool you need for whatever car you have in the coming years.

If you're AFR's are really 13 under load then expect to see some overheated spark plug colours too.

The Walbro is a high "flow" pump, the pressure is maintained by the FPR.
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Funny you should say that as, my brothers just starting to get into remapping with his Evo and, he'd mentioned spliting the cost of a wideband lambda monitor with me ! I like the Innovative Motorsports LC1 for simplicity but, the PLX devices R500 for features. I'll get on to him and see what he thinks.

Also, as you've said, if the AFR's were that low, I would see it in the spark plugs and, teh last time I checked them, they were just as you'd expect them to be from running good AFR's !
One thing I will say though is that I took the car for a little run at the weekend and the exhaust gas temps seemed to be lower (200-250 degrees F lower) and, they dropped quicker too !
So, I do think the new fuel pump has improved matters but, I just want to know if I'd see any benefit in replacing the FPR ?

Your comment on the fuel pressure, controlled by the FPR, is what I expected and always been led to believe too !
 
campbellju

campbellju

Moderators
Staff member
youngsyp said:
So, I do think the new fuel pump has improved matters but, I just want to know if I'd see any benefit in replacing the FPR
Click to expand...
It only takes 30 minutes so you may as well try it.
 
Y

youngsyp

Active Member
campbellju said:
It only takes 30 minutes so you may as well try it.
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Again, you're right. The only problem I foresee is the fixing screws. In the past, I haven't been able to shift them for love nor money ! Any pointers ?
 
vss irvine

vss irvine

Well-Known Member
cut a slot in the heads of them, allowing you to use a large flat head screwdriver. or if your careful you could use a small impact driver just to crack them?
 
Y

youngsyp

Active Member
Thanks mate.

I've got an angled screw driver that I'll try giving a whack with a hammer. That should crack any seal they've formed. If that doesn't work, I'll try your slotting idea !
 
Y

youngsyp

Active Member
antgtir said:
I presume that now you state the problem is fixed was it the FPR?

Ant.
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Ant, I used the word 'fixed', with a question mark. ;-)
I won't know it's been fixed or not, if indeed there was a problem in the first place, until I can check the AFR's !
Basically, the point behind this thread, was to see if my FPR was ok. As it's reading 3.3bar or there abouts at idle, with vacuum disconnected, I think it could be a bit tired. The car has done 93000 miles so, I guess I shouldn't be surprised.

I'm gonna try and replace it tonight, with another FPR I have and see what the base fuel pressure is then. If it's 3bar, the current FPR, would indeed appear to be tired !

By the way, has anyone in the Milton Keynes area got a timing light I can borrow ?

My one's at my parents house in Essex ! :doh:
 
antgtir

antgtir

New Member
youngsyp said:
Ant, I used the word 'fixed', with a question mark. ;-)
I won't know it's been fixed or not, if indeed there was a problem in the first place, until I can check the AFR's !
Basically, the point behind this thread, was to see if my FPR was ok. As it's reading 3.3bar or there abouts at idle, with vacuum disconnected, I think it could be a bit tired. The car has done 93000 miles so, I guess I shouldn't be surprised.

I'm gonna try and replace it tonight, with another FPR I have and see what the base fuel pressure is then. If it's 3bar, the current FPR, would indeed appear to be tired !

By the way, has anyone in the Milton Keynes area got a timing light I can borrow ?

My one's at my parents house in Essex ! :doh:
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I saw the question mark after i posted and couldn't be bothered changing it lol:lol:

I got excited as i thought the issues im having at the mo were being experienced by you and you had solved the prob fr me lol:lol:

I must admit i will be changing the fuel pump very soon and hard wiring the live feed from the battery and a nice new earth, another job to then strike off the list after all the other elec bits ive done:roll: :lol:

Ant.
 
Y

youngsyp

Active Member
antgtir said:
I must admit i will be changing the fuel pump very soon and hard wiring the live feed from the battery and a nice new earth, another job to then strike off the list after all the other elec bits ive done:roll: :lol:

Ant.
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It's definitely worth doing as, for some reason, Nissan restrict the voltage to the fuel pump to just over 12 volts. Having seen the pump and the big '12v' stamped on it, I wonder if that's why and, if sending it the full 14.4v, will wear the stock pump out quicker ?!

With the new Walbro pump, you don't need to worry about voltages and infact, as the flow figures for the Walbro are given at 12v, with the full 14.4v, you'll be able to supply more than 255 lph. So, it'll give you a excellent starting point for a butch fuel system, good enough up to silly power levels !

I just hope your rubber pipe work between the tank and metal pipe are in better condition than mine was as, it took me 5 hours of swearing and battering my hands to replace that mofo yesterday ! All for 6 inches of rubber pipe ! :doh:
 
Y

youngsyp

Active Member
Right, changed the FPR over and............. I got exactly the same readings ! :lol:

Me thinks the FPR is working as it should but, the gauge is reading incorrectly ?!

Any other idea's chaps ?

Should have my timing light in a day or two so, I can check the timing then. Although, it's not moved from the last I checked it and, still has the factory 'seal' on the upper bolt so, I don't expect that to be any different !
 
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